Microwave enhanced advanced oxidation treatment of dairy manure.

The microwave enhanced advanced oxidation process (MW-AOP) was used to treat dairy manure in a continuous-flow 915 MHz microwave wastewater treatment system. The treatment efficiency increased with an increase in temperature, as well as hydrogen peroxide dosage. The settling property was also improved in all treated sets, regardless of temperature applied. The system operated at temperatures >100 °C had a much higher soluble chemical oxygen demand than at temperatures <100 °C. The highest soluble carbonaceous compounds, orthophosphate and ammonia were obtained at 110 °C and 0.6%H2O2 per % of total solids content. The process should be operated at higher temperatures and higher hydrogen peroxide dosages for maximizing solids disintegration, nutrient release and energy efficiency. An energy fingerprint correlating the cumulative energy consumption and temperature rise was developed. The results demonstrated that the custom designed MW-AOP system is suitable for the effective treatment of dairy manure. The system can readily be scaled up and integrated into a dairy farm manure treatment and resource recovery system.

Operational strategy for nitrogen removal from centrate in a two-stage partial nitrification--anammox process.

This paper presents the operational strategy for nitrogen removal in a two-stage, partial nitrification (PN) process coupled with anaerobic ammonium oxidation (Anammox) process. The process was used to remove ammonium from centrate obtained from a full-scale, wastewater treatment plant in British Columbia, Canada. The PN, which was carried out in a sequencing batch reactor (SBR), successfully converted approximately 49.5 +/- 1.0% of ammonium to nitrite. The operation of SBR under higher dissolved oxygen in combination with slow feeding resulted in significant reduced HRT without nitrate accumulation. Partially nitrified centrate was further treated in Anammox reactors, where the mixture of ammonium and nitrite was converted mainly to nitrogen gas. Anammox treatment was carried out in two different types of Anammox reactors: a moving bed hybrid reactor and an up-flow fixed-bed biofilm reactor. The hybrid Anammox reactor removed an average of 55.8% of NH4-N, versus the 48.3% NH4-N removed in the up-flow fixed-bed reactor. Nitrite removal in the hybrid and up-flow fixed-bed Anammox reactors averaged 80.8% and 62.5%, respectively. This study also illustrated that in both Anammox reactors, better ammonium removal was achieved when the nitrite to ammonium ratio is between 1.35 and 1.45. As such, alkalinity was found to neither control nor limit the Anammox reaction.

Effects of irradiation intensity and pH on nutrients release and solids destruction of waste activated sludge using the microwave-enhanced advanced oxidation process.

Using the microwave-enhanced advanced oxidation process (MW/H2O2-AOP), the pH and irradiation intensity on waste activated sludge samples were investigated to provide insight to the athermal effects on nutrients release, solids destruction, particle size distribution and dewaterability, and to demonstrate their interrelationships. Carbonaceous matters and nutrients released into solution depended on the irradiation intensity and time. Higher irradiation levels tended to be more effective in the solubilization of nutrients and had more pronounced effects in the dewaterability of sludge. In terms of particle size distribution, detectable particles increased in size for treatments in acidic conditions, while the dewaterability of treated sludge was improved. In treatments under neutral and alkaline conditions, the particle size range increased, with more small particles formed, thereby significantly deteriorating the dewaterability of sludge treated in alkaline conditions. The best results for the solubilization of nutrients were in alkaline conditions with high irradiation power, but dewaterability of the sludge was compromised. Sludge treatment with the MW/H2O2-AOP in acidic conditions with high irradiation power yielded the best dewaterable sludge and significant nutrient solubilization; therefore, it is the recommended treatment condition for activated sludge.

Extraction of nutrients from foam in a membrane activated sludge system.

This study investigated the feasibility of treating the foams generated in enhanced biological phosphorus removal processes with the microwave-enhanced advanced oxidation process to reduce solids and solubilize nutrients for recovery purposes. It was found that more than half of the total chemical oxygen demand was solubilized during the treatment with just a small dose of hydrogen peroxide, signifying effective destruction of foam solids. Significant solubilization of phosphates, volatile fatty acids and ammonia was also observed, along with the release of metals contained in the foam, including calcium, potassium, and magnesium, which thereby represents additional potential benefits for nutrient recovery via subsequent crystallization processes. Since the solids content of foam is typically high, pretreatment for thickening sludge solids is not necessary prior to the use of microwave-enhanced advanced oxidation processes. As a result, this also offers further potential for reduction of energy costs. The process could be an efficient method for the removal and control of foam and the recovery of all available phosphorus at the same time.

Production and basic morphology of struvite crystals from a pilot-scale crystallization process.

A pilot-scale, struvite crystallization process was operated using anaerobic digester supernatants from two, full-scale, treatment plants as influent. It was found that the produced struvite crystals were easily separated from the process and were composed of very pure struvite (91.2 % to 94.1 % purity), with small amounts of calcium and carbonate, and traces of iron and aluminum. Most of the harvested struvite crystals, which were an aggregation of numerous fine crystals, were round, hard and larger than 1.5 mm in mean diameter. The crystal retention time in the reactor and the magnesium dosage in the supernatant appeared to have a significant effect on the crystal size, hardness and morphology.

Disinfection and solubilization of sewage sludge using the microwave enhanced advanced oxidation process.

The microwave enhanced advanced oxidation process (MW/H(2)O(2)-AOP) was used to treat municipal sewage sludge for solids disintegration, nutrient solubilization, with an emphasis on pathogen destruction and regrowth. Pathogen reduction, in terms of fecal coliform concentrations were found below detection limit (1000 CFU/L) immediately after treatment when sludge was treated at 70 degrees C with more than 0.04% of H(2)O(2) (w/w). Significant regrowth of fecal coliforms was observed for the treated samples after 72 h. However, no regrowth was observed for samples treated at 70 degrees C with 0.08% H(2)O(2) or higher, suggesting a complete elimination of fecal coliforms. The range of hydrogen peroxide used did not have a significant effect on orthophosphate release regardless of temperature. Ammonia release at these low temperatures was found to be insignificant. The soluble chemical oxygen demand increased with an increase of hydrogen peroxide dosage at 70 degrees C. However, there was no clear trend of soluble chemical oxygen demand over varying hydrogen peroxide dosage at 55 degrees C. The MW/H(2)O(2)-AOP is a novel process for the pasteurization and stabilization of sewage sludge to meet and maintain Class A biosolids criteria.

Degradation of greenhouse twines derived from natural fibers and biodegradable polymer during composting.

Commercial composting operations generally do not accept organic wastes with plastic twines from the greenhouse vegetable industry and the bulk of the waste materials ends up in landfills. The objectives of this paper are to identify environmentally compatible substitutes that could replace the current use of petrochemically derived plastic twines in greenhouse vegetable production, thus diverting them from landfills, and to assess the extent of their degradation via composting. Physical properties of the twines, including linear density, percent weight loss and tensile strength were monitored for the biodegradation tests. A pilot-scale composting trial was conducted in an in-vessel composting system. Results showed that the three biodegradable twine materials (cotton, jute and EcoPLA) could degrade readily in a composting environment within a reasonable time frame. Specifically, at the end of 105 days of composting, 85.3%, 84.8% and 81.1% of weight loss was observed for cotton, jute and EcoPLA, respectively. Furthermore, EcoPLA exhibited a slower decline in tensile strength with time, when compared to jute and cotton.

Rapid determination of total Kjeldahl nitrogen using microwave digestion.

A closed-vessel microwave digestion process for the determination of total Kjeldahl nitrogen (TKN) has been developed for sewage and wastewater. TKN values obtained from the microwave digestion method were in excellent agreement with those of the thermal digestion method. The accuracy of both analytical methods is comparable. In comparison to the conventional thermal digestion, the microwave method shortened the time required for complete digestion from 4 h to 25 min, and also decreased the maximum digestion temperature from 380 degrees C to 200 degrees C. This developed method may contribute to a significant reduction in sample digestion time, resulting in an increase in analytical throughput. The microwave digestion method developed in this study could be a rapid and efficient means for TKN determination for sewage wastewater and sludge.

Methane production using whole and screened dairy manure in conventional and fixed-film reactors.

The technical feasibility of adopting the fixed-film reactor concept for biogas production from screened dairy manure was investigated. The methane production capability of laboratory-scale 4-L anaerobic reactors (conventional and fixed-film) receiving screened dairy manure and operated at 35 degrees C was compared. Dairy manure filtrate with 4.4% total solids (TS) and 3.4% volatile solids (VS) (average value) was prepared from 1:1 manure-water slurry. The feed material was added intermittently at loading rates ranging from 2.34 to 25 and 2.25 to 785 g VS/L d, respectively, for the conventional and fixed-film reactors. Maximum methane production rate (L CH(4)/L d) for the conventional reactor was 0.63 L CH(4)/L d achieved at a 6-day hydraulic retention time (HRT). For the fixed-film reactor the maximum production rate was 3.53 L CH(4)/L d when operated at a loading rate of 262 g VS/L d (3 h HRT). The fixed-film reactor was capable of sustaining a loading of 785 g VS/L d (1 h HRT). The fixed-film reactor performed much better than the conventional reactors. These results indicate that a large reduction of required reactor volume is possible through application of a fixed-film concept combined with a liquid-solid separation pretreatment of dairy manure.

Ammonia removal from compost leachate using zeolite. II. A study using continuous flow packed columns.

Bench-scale packed zeolite columns were set up and operated to investigate the continuous removal of ammonium ions from compost leachate. The effects of hydraulic retention time (HRT), and particle size of the zeolite on the ammonia adsorption capacity were studied. For both the coarse particle and the powdered zeolite columns, higher ammonia removal efficiencies were achieved with longer HRT (i.e., lower influent flow rate) tests. At the same HRT, ammonia removal efficiencies from tests with powdered zeolite were generally 20% higher than tests with the coarse particle zeolite. A HRT of 6 hours was found appropriate for efficient ammonia removal, and an operating capacity of 1.31 mg N/g zeolite was obtained. Over 98% of the ammonia input from the influent was consistently removed for over 5 bed volumes (BV) of compost leachate flowing through the zeolite column. Zeolite proved to have a great potential as a medium for ammonia removal in treating composting leachate.

Ammonia removal from composting leachate using zeolite. I. Characterization of the zeolite.

The effects of ammonium concentrations, contact time, and zeolite particle sizes on the ammonium adsorption capacities of a Canadian zeolite were studied using batch experiments. Both the rates and capacities of ammonium adsorption increased with increased concentrations of ammonium in solution. Ammonium adsorption increased significantly with decreasing zeolite particle size for all tests and the adsorption capacities ranged from 14.35-17.81 mg N/g. Also, ammonia adsorption increased with contact time, and it occurred rapidly at the beginning of contact, and then gradually decreased as time progressed. Langmuir isotherm best describes the equilibrium of ammonia adsorption on zeolite. Particle diffusion was the rate-controlling mechanism for the first 4 h of contact. In spite of competition potassium ions, zeolite has shown a great potential for ammonia removal from composting leachates.

Ammonia removal from compost leachate using zeolite. III. Regeneration of zeolite columns.

The effects of hydraulic reteneration time (HRT), and the strength of the regenerating solution on the ammonia adsorption capacity and the zeolite regeneration were studied using bench-scale packed zeolite columns. A 0.6 M NaCl solution fed at a HRT of I h was preferred for the regeneration process, and more than 95% of adsorbed ammonium ions were recovered after using 7-8 bed volumes (BV) of the regenerating solution. The adsorption-regeneration time ratio was approximately 5:1. High concentration of potassium ions in the composting leachate competed with NH4+ ions for the exchange sites, resulting in a reduction in the efficiencies of ammonia removal and zeolite column regeneration. However, Zeolite still proved to have a great potential as a medium for ammonia removal in treating composting leachate.

Activated sludge immobilization using the PVA-alginate-borate method.

The PVA-alginate-borate method was used successfully to immobilize activated sludge. The optimum polyvinyl alcohol (PVA) concentration in the immobilized sludge was determined to be 10-12.5%. A minimal alginate of 1% in the beads was needed to prevent bead agglomeration. If the pH of the saturated boric acid was adjusted to 7.0 prior to allowing droplets of the mixture of PVA, alginate and sludge to enter the solution, a high level of sludge activity could be maintained in the beads formed. During the continuous operation of a fluidized bed reactor, with hydraulic retention time (HRT) in the range of 24-3 h (BOD loading from 0.176 to 0.766 kg/d/m3) and an aeration rate at 1.0 L/min, more than 90% of BOD5, NH4(+)-N and TKN were removed. The immobilized sludge exhibited satisfactory mechanical stability without apparent breakage.

Treatment of greenhouse wastewater using constructed wetlands.

Five wetland designs, based on conventional surface flow (SF) and subsurface flow (SSF) approaches, were assessed for nitrogen and phosphorus removal from greenhouse wastewater. Results indicated none of the individual designs assessed was capable of providing the highest treatment effect for all nutrients of concern; however, the SF wetland emerged as the most appropriate design for the treatment of greenhouse wastewater. The highest mean phosphorus reduction of 65% was observed in the unplanted SF wetlands. Peak nitrate reductions of 54% were observed in the 15-cm deep SF wetlands and ammonia removal of 74% was achieved in the unplanted SF wetlands. Nitrate concentration in the greenhouse effluent can be reduced to acceptable levels for the protection of freshwater aquatic life (i.e., less then 40 ppm) using a loading rate of 1.65 g NO3-N/m2/day and a design water depth of 30 cm or greater. Based on available literature and the results of this research project, a multistage design, consisting of an unplanted pre-treatment basin followed by a 25 to 35 cm deep surface flow marsh with open water components, is recommended.

Domestic wastewater treatment using immobilized sludge fluidized-bed reactors.

Bench-scale fluidized-bed reactors using the immobilized activated sludge process were studied for the treatment of domestic wastewater. Different intermittent aeration patterns were investigated in order to improve the total nitrogen (TN) removal. The best TN removal at 74.4% was achieved at an HRT of 6 hours (with corresponding BOD loading rate of 0.766 kg/m3/d) and an aeration-pattern of 1,3 (the hours of aeration and non-aeration time cycle). The removal efficiencies for organic carbon, NH4(+)-N, TKN and TSS were not affected and remained at more than 90%. Simultaneous organic carbon and nitrogen removal was accomplished in a single immobilized sludge reactor. The impact of various influent feed patterns on the treatment was examined. The continuous feed pattern was recommended as it ensured good TN removal without any adverse impacts on the removal of organic carbon, NH4(+)-N, TKN and TSS. The immobilized sludge beads exhibited satisfactory mechanical stability without apparent breakage over the 180-day experiment period.

Acidogenic fermentation of lactose.

Cheese whey is the main component of waste streams from cheese manufacturing plants. Whey is a high biochemical oxygen demand (BOD) effluent that must be reduced before the streams are sent to the sewer. It is proposed in this article that the production of methane by anaerobic fermentation would be the best use of this stream, especially for small plants. Single-stage fermentation of lactose, the main component of whey, results in a very low pH and a stalled process. Two-phase fermentation will eliminate this problem. The acidogenic stage of fermentation has been studied at pH of between 4 and 6.5. The nature of the main products of the reaction have been found to be pH dependent. Below a pH of 4.5 a gas (CO(2) and H(2)) is produced along with ethanol, acetate, and butyrate. Above a pH of 4.5 no gas was produced, and the liquid products included less ethanol and butyrate and more acetate. A separate study on the conditions for gas formation showed that if the pH dropped for a short time below 4.5 gases were formed at all subsequent pH. This would indicate a change in population distribution due to the period at a low pH. By assuming that the desired products from the acidogenic stage were butyrate, acetate, and no gases, the optimum pH range was found to be between 6.0 and 6.5.

Kinetics of whey-lactose acidogenesis.

The mixed-culture anaerobic conversion of lactose to organic acids in a bench-scale continuous-flow stirredtank fermentor is considered. The major acidogenic end-product distribution with respect to the dilution rate are presented. A Monod chemostat model is employed to describe a microbial growth, and the influence on pH of the estimated model parameters is discussed.

Influence of dilution rate on the acidogenic phase products distribution during two-phase lactose anaerobiosis.

Acidogenic fermentation of lactose was carried out in a continuous stirred reactor with a mixed anaerobic culture. From the variation of the reactor products with pH and dilution rate two possible carbon flow schemes were proposed for the reaction. In both schemes the carbon flow from pyruvate to butyrate and lactate was assumed to occur in parallel. A change in gas composition and in product concentrations at dilution rates between 0.1 and 0.15 h(-1) for pH levels between 4.5 and 6.0 was ascribed to a shift in microbial population. To clarify the mechanism radiotracer tests were made using [U-(14)C]-butyrate, [2-(14)C]-propionate and [U-(14)C]-lactate to determine the path of carbon flow during acidogenesis of lactose using a mixed culture. At a dilution rate between 0.1 and 0.15 h(-1) and pH from 4.5 to 6.0 a rise in the lactate concentration in the product was shown to be due to a microbial population shift which disabled the conversion of lactate to other intermediary metabolites. It was also found that the flow of carbon from pyruvate to butyrate and lactate occurred by parallel pathways. Also, in the presence of hydrogen reducing methanogens, lactate was almost completely converted to acetate and not propionate. Butyrate was found to be converted to acetate at a slow rate as long as hydrogen reducing methanogens were present. The role played by propionibacteria in this lactose acidogenic eocosystem was minor. From the carbon flow model it can be concluded that lactate is the most suitable marker for optimizing an acidogenic reactor in a two-phase biomethanation process.

Influence of whey protein on continuous acidogenic degradation of lactose.

In previous studies on the acidogenic phase of anaerobic fermentation of lactose, a pathway for the reaction and a rate equation have been proposed. The question then remained as to the effect of the protein in whole whey on the mechanism and on the overall organic substrate conversion. In this study, it was found that as much as 70% of the protein was broken down in the acidogenic reactor. Radiotracer tests showed that the inclusion of protein had no effect on the reaction pathway for lactose degradation. Thus, the whole sweet cheese whey can be fermented as efficiently as whey from which the protein has been removed.

The relationship between hydrogen gas and butanol production by Clostridium saccharoperbutylacetonicum.

Two simultaneous fermentations were performed at 26 degrees C with simultaneous inocula using Clostridium saccharoperbutylacetonicum. Fermentation 1 prevented the gas formed by the biomass from escaping the fermentor while 2 allowed the gas formed to escape. Fermentor 1 provided for the production of butanol, acetone, and ethanol, while when the H(2) formed was allowed to escape with fermentor 2, neither butanol nor acetone were produced. Ethanol was also formed in both fermentors and began along with the initial growth of biomass and continued until the fermentations were complete. Butanol and acetone production began after biomass growth had reached a maximum and began to subside. The butanol-acetone-ethanol millimolar yields and ratios were 38:1:14 respectively. The fermentor 2 results show that a yield of 2.1 L H(2), 93 or 370 mmol H(2)/mol glucose, was formed only during the growing stage of growth; neither butanol nor acetone were produced; ethanol was formed throughout the fermentation, reaching a yield of 15.2 mmolar. It appears that hydrogen gas is required for butanol production during the resting stage of growth.